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Abstract
The inability to recover functions lost after severe spinal cord injury has been recognized for millennia and was first attributed to a failure of spinal cord neural regeneration over 100 years ago. The last forty years have seen intense research into achieving such regeneration, but in spite of conceptual advances and many reports announcing successful interventions, progress has been slow and often controversial. Here, I examine consequential advances and setbacks, and critically consider assumptions underlying certain approaches. I argue that expanding mechanistic knowledge about multiple forms of neural regeneration, why they fail and how they can restore function will resolve conceptual contentions and push the field forward.
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52
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Roy JP, Halford MM, Stacker SA. The biochemistry, signalling and disease relevance of RYK and other WNT-binding receptor tyrosine kinases. Growth Factors 2018; 36:15-40. [PMID: 29806777 DOI: 10.1080/08977194.2018.1472089] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The receptor tyrosine kinases (RTKs) are a well-characterized family of growth factor receptors that have central roles in human disease and are frequently therapeutically targeted. The RYK, ROR, PTK7 and MuSK subfamilies make up an understudied subset of WNT-binding RTKs. Numerous developmental, stem cell and pathological roles of WNTs, in particular WNT5A, involve signalling via these WNT receptors. The WNT-binding RTKs have highly context-dependent signalling outputs and stimulate the β-catenin-dependent, planar cell polarity and/or WNT/Ca2+ pathways. RYK, ROR and PTK7 members have a pseudokinase domain in their intracellular regions. Alternative signalling mechanisms, including proteolytic cleavage and protein scaffolding functions, have been identified for these receptors. This review explores the structure, signalling, physiological and pathological roles of RYK, with particular attention paid to cancer and the possibility of therapeutically targeting RYK. The other WNT-binding RTKs are compared with RYK throughout to highlight the similarities and differences within this subset of WNT receptors.
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Affiliation(s)
- James P Roy
- a Tumour Angiogenesis and Microenvironment Program , Peter MacCallum Cancer Centre , Melbourne , Australia
- b Sir Peter MacCallum Department of Oncology , The University of Melbourne , Parkville , Australia
| | - Michael M Halford
- a Tumour Angiogenesis and Microenvironment Program , Peter MacCallum Cancer Centre , Melbourne , Australia
| | - Steven A Stacker
- a Tumour Angiogenesis and Microenvironment Program , Peter MacCallum Cancer Centre , Melbourne , Australia
- b Sir Peter MacCallum Department of Oncology , The University of Melbourne , Parkville , Australia
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53
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Sarin S, Zuniga-Sanchez E, Kurmangaliyev YZ, Cousins H, Patel M, Hernandez J, Zhang KX, Samuel MA, Morey M, Sanes JR, Zipursky SL. Role for Wnt Signaling in Retinal Neuropil Development: Analysis via RNA-Seq and In Vivo Somatic CRISPR Mutagenesis. Neuron 2018; 98:109-126.e8. [PMID: 29576390 DOI: 10.1016/j.neuron.2018.03.004] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 01/16/2018] [Accepted: 03/02/2018] [Indexed: 12/22/2022]
Abstract
Screens for genes that orchestrate neural circuit formation in mammals have been hindered by practical constraints of germline mutagenesis. To overcome these limitations, we combined RNA-seq with somatic CRISPR mutagenesis to study synapse development in the mouse retina. Here synapses occur between cellular layers, forming two multilayered neuropils. The outer neuropil, the outer plexiform layer (OPL), contains synapses made by rod and cone photoreceptor axons on rod and cone bipolar dendrites, respectively. We used RNA-seq to identify selectively expressed genes encoding cell surface and secreted proteins and CRISPR-Cas9 electroporation with cell-specific promoters to assess their roles in OPL development. Among the genes identified in this way are Wnt5a and Wnt5b. They are produced by rod bipolars and activate a non-canonical signaling pathway in rods to regulate early OPL patterning. The approach we use here can be applied to other parts of the brain.
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Affiliation(s)
- Sumeet Sarin
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02130, USA
| | - Elizabeth Zuniga-Sanchez
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Yerbol Z Kurmangaliyev
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Henry Cousins
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02130, USA
| | - Mili Patel
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02130, USA
| | - Jeanette Hernandez
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Kelvin X Zhang
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Melanie A Samuel
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02130, USA
| | - Marta Morey
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Joshua R Sanes
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02130, USA.
| | - S Lawrence Zipursky
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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54
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Cortico-reticulo-spinal circuit reorganization enables functional recovery after severe spinal cord contusion. Nat Neurosci 2018; 21:576-588. [PMID: 29556028 DOI: 10.1038/s41593-018-0093-5] [Citation(s) in RCA: 184] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 01/15/2018] [Indexed: 12/24/2022]
Abstract
Severe spinal cord contusions interrupt nearly all brain projections to lumbar circuits producing leg movement. Failure of these projections to reorganize leads to permanent paralysis. Here we modeled these injuries in rodents. A severe contusion abolished all motor cortex projections below injury. However, the motor cortex immediately regained adaptive control over the paralyzed legs during electrochemical neuromodulation of lumbar circuits. Glutamatergic reticulospinal neurons with residual projections below the injury relayed the cortical command downstream. Gravity-assisted rehabilitation enabled by the neuromodulation therapy reinforced these reticulospinal projections, rerouting cortical information through this pathway. This circuit reorganization mediated a motor cortex-dependent recovery of natural walking and swimming without requiring neuromodulation. Cortico-reticulo-spinal circuit reorganization may also improve recovery in humans.
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55
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Hilton BJ, Bradke F. Can injured adult CNS axons regenerate by recapitulating development? Development 2017; 144:3417-3429. [PMID: 28974639 DOI: 10.1242/dev.148312] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In the adult mammalian central nervous system (CNS), neurons typically fail to regenerate their axons after injury. During development, by contrast, neurons extend axons effectively. A variety of intracellular mechanisms mediate this difference, including changes in gene expression, the ability to form a growth cone, differences in mitochondrial function/axonal transport and the efficacy of synaptic transmission. In turn, these intracellular processes are linked to extracellular differences between the developing and adult CNS. During development, the extracellular environment directs axon growth and circuit formation. In adulthood, by contrast, extracellular factors, such as myelin and the extracellular matrix, restrict axon growth. Here, we discuss whether the reactivation of developmental processes can elicit axon regeneration in the injured CNS.
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Affiliation(s)
- Brett J Hilton
- Laboratory for Axon Growth and Regeneration, German Centre for Neurodegenerative Diseases (DZNE), Sigmund-Freud-Strasse 27, 53127, Bonn, Germany
| | - Frank Bradke
- Laboratory for Axon Growth and Regeneration, German Centre for Neurodegenerative Diseases (DZNE), Sigmund-Freud-Strasse 27, 53127, Bonn, Germany
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56
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Filous AR, Schwab JM. Determinants of Axon Growth, Plasticity, and Regeneration in the Context of Spinal Cord Injury. THE AMERICAN JOURNAL OF PATHOLOGY 2017; 188:53-62. [PMID: 29030051 DOI: 10.1016/j.ajpath.2017.09.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2017] [Revised: 09/15/2017] [Accepted: 09/21/2017] [Indexed: 12/30/2022]
Abstract
The mechanisms that underlie recovery after injury of the central nervous system have rarely been definitively established. Axon regrowth remains the major prerequisite for plasticity, regeneration, circuit formation, and eventually functional recovery. The attributed functional relevance of axon regrowth, however, will depend on several subsequent conditional neurobiological modifications, including myelination and synapse formation, but also pruning of aberrant connectivity. Despite the ability to revamp axon outgrowth by altering an increasing number of extracellular and intracellular targets, disentangling which axons are responsible for the recovery of function from those that are functionally silent, or even contributing to aberrant functions, represents a pertinent void in our understanding, challenging the intuitive translational link between anatomical and functional regeneration. Anatomic hallmarks of regeneration are not static and are largely activity dependent. Herein, we survey mechanisms leading to the formation of dystrophic growth cone at the injured axonal tip, the subsequent axonal dieback, and the molecular determinants of axon growth, plasticity, and regeneration in the context of spinal cord injury.
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Affiliation(s)
- Angela R Filous
- Spinal Cord Injury Division, Department of Neurology, The Ohio State University, Wexner Medical Center, Columbus, Ohio.
| | - Jan M Schwab
- Spinal Cord Injury Division, Department of Neurology, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Department of Neuroscience, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Department of Physical Medicine and Rehabilitation, The Ohio State University, Wexner Medical Center, Columbus, Ohio; Center for Brain and Spinal Cord Repair, Spinal Cord Injury Medicine, The Ohio State University, Wexner Medical Center, Columbus, Ohio.
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57
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Brafman D, Willert K. Wnt/β-catenin signaling during early vertebrate neural development. Dev Neurobiol 2017; 77:1239-1259. [PMID: 28799266 DOI: 10.1002/dneu.22517] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 07/24/2017] [Accepted: 08/09/2017] [Indexed: 12/29/2022]
Abstract
The vertebrate central nervous system (CNS) is comprised of vast number of distinct cell types arranged in a highly organized manner. This high degree of complexity is achieved by cellular communication, including direct cell-cell contact, cell-matrix interactions, and cell-growth factor signaling. Among the several developmental signals controlling the development of the CNS, Wnt proteins have emerged as particularly critical and, hence, have captivated the attention of many researchers. With Wnts' evolutionarily conserved function as primordial symmetry breaking signals, these proteins and their downstream effects are responsible for simultaneously establishing cellular diversity and tissue organization. With their expansive repertoire of secreted agonists and antagonists, cell surface receptors, signaling cascades and downstream biological effects, Wnts are ideally suited to control the complex processes underlying vertebrate neural development. In this review, we will describe the mechanisms by which Wnts exert their potent effects on cells and tissues and highlight the many roles of Wnt signaling during neural development, starting from the initial induction of the neural plate, the subsequent patterning along the embryonic axes, to the intricately organized structure of the CNS. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1239-1259, 2017.
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Affiliation(s)
- David Brafman
- School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona, 85287
| | - Karl Willert
- Department of Cellular & Molecular Medicine, University of California San Diego, La Jolla, CA, 92093-0695
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58
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A Corticocortical Circuit Directly Links Retrosplenial Cortex to M2 in the Mouse. J Neurosci 2017; 36:9365-74. [PMID: 27605612 DOI: 10.1523/jneurosci.1099-16.2016] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2016] [Accepted: 07/24/2016] [Indexed: 01/09/2023] Open
Abstract
UNLABELLED Retrosplenial cortex (RSC) is a dorsomedial parietal area involved in a range of cognitive functions, including episodic memory, navigation, and spatial memory. Anatomically, the RSC receives inputs from dorsal hippocampal networks and in turn projects to medial neocortical areas. A particularly prominent projection extends rostrally to the posterior secondary motor cortex (M2), suggesting a functional corticocortical link from the RSC to M2 and thus a bridge between hippocampal and neocortical networks involved in mnemonic and sensorimotor aspects of navigation. We investigated the cellular connectivity in this RSC→M2 projection in the mouse using optogenetic photostimulation, retrograde labeling, and electrophysiology. Axons from RSC formed monosynaptic excitatory connections onto M2 pyramidal neurons across layers and projection classes, including corticocortical/intratelencephalic neurons (reciprocally and callosally projecting) in layers 2-6, pyramidal tract neurons (corticocollicular, corticopontine) in layer 5B, and, to a lesser extent, corticothalamic neurons in layer 6. In addition to these direct connections, disynaptic connections were made via posterior parietal cortex (RSC→PPC→M2) and anteromedial thalamus (RSC→AM→M2). In the reverse direction, axons from M2 monosynaptically excited M2-projecting corticocortical neurons in the RSC, especially in the superficial layers of the dysgranular region. These findings establish an excitatory RSC→M2 corticocortical circuit that engages diverse types of excitatory projection neurons in the downstream area, suggesting a basis for direct communication from dorsal hippocampal networks involved in spatial memory and navigation to neocortical networks involved in diverse aspects of sensorimotor integration and motor control. SIGNIFICANCE STATEMENT Corticocortical pathways interconnect cortical areas extensively, but the cellular connectivity in these pathways remains largely uncharacterized. Here, we show that a posterior part of secondary motor cortex receives corticocortical axons from the rostral retrosplenial cortex (RSC) and these form monosynaptic excitatory connections onto a wide spectrum of excitatory projection neurons in this area. Our results define a cellular basis for direct communication from RSC to this medial frontal area, suggesting a direct link from dorsal hippocampal networks involved in spatial cognition and navigation (the "map") to sensorimotor networks involved the control of movement (the "motor").
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59
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The Wnt receptor Ryk is a negative regulator of mammalian dendrite morphogenesis. Sci Rep 2017; 7:5965. [PMID: 28729735 PMCID: PMC5519545 DOI: 10.1038/s41598-017-06140-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 05/17/2017] [Indexed: 12/23/2022] Open
Abstract
The unique dendritic architecture of a given neuronal subtype determines its synaptic connectivity and ability to integrate into functional neuronal networks. It is now clear that abnormal dendritic structure is associated with neuropsychiatric and neurodegenerative disorders. Currently, however, the nature of the extrinsic factors that limit dendritic growth and branching within predetermined boundaries in the mammalian brain is poorly understood. Here we identify the Wnt receptor Ryk as a novel negative regulator of dendritic arborisation. We demonstrate that loss of Ryk in mouse hippocampal and cortical neurons promotes excessive dendrite growth and branching in vitro. Conversely, overexpression of wildtype Ryk restricts these processes, confirming that Ryk acts to restrain dendrite arborisation. Furthermore, we identify a hitherto uncharacterized membrane proximal subdomain crucial for Ryk-mediated suppression of dendrite morphogenesis, suggesting that it may act through a novel signalling pathway to constrain dendrite complexity. We also demonstrate that Ryk performs a similar function in vivo as Ryk haploinsufficient postnatal animals exhibit excessive dendrite growth and branching in layer 2/3 pyramidal neurons of the somatosensory cortex. These findings reveal an essential role for Ryk in regulating dendrite complexity and raise the intriguing possibility that it may influence neural plasticity by modifying dendritic structure.
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60
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Kaplan A, Bueno M, Hua L, Fournier AE. Maximizing functional axon repair in the injured central nervous system: Lessons from neuronal development. Dev Dyn 2017. [PMID: 28643358 DOI: 10.1002/dvdy.24536] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The failure of damaged axons to regrow underlies disability in central nervous system injury and disease. Therapies that stimulate axon repair will be critical to restore function. Extensive axon regeneration can be induced by manipulation of oncogenes and tumor suppressors; however, it has been difficult to translate this into functional recovery in models of spinal cord injury. The current challenge is to maximize the functional integration of regenerating axons to recover motor and sensory behaviors. Insights into axonal growth and wiring during nervous system development are helping guide new approaches to boost regeneration and functional connectivity after injury in the mature nervous system. Here we discuss our current understanding of axonal behavior after injury and prospects for the development of drugs to optimize axon regeneration and functional recovery after CNS injury. Developmental Dynamics 247:18-23, 2018. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Andrew Kaplan
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montréal, Québec, Canada
| | - Mardja Bueno
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montréal, Québec, Canada
| | - Luyang Hua
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montréal, Québec, Canada
| | - Alyson E Fournier
- Department of Neurology and Neurosurgery, Montréal Neurological Institute, McGill University, Montréal, Québec, Canada
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61
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Manohar A, Foffani G, Ganzer PD, Bethea JR, Moxon KA. Cortex-dependent recovery of unassisted hindlimb locomotion after complete spinal cord injury in adult rats. eLife 2017; 6. [PMID: 28661400 PMCID: PMC5499944 DOI: 10.7554/elife.23532] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2016] [Accepted: 06/22/2017] [Indexed: 12/29/2022] Open
Abstract
After paralyzing spinal cord injury the adult nervous system has little ability to ‘heal’ spinal connections, and it is assumed to be unable to develop extra-spinal recovery strategies to bypass the lesion. We challenge this assumption, showing that completely spinalized adult rats can recover unassisted hindlimb weight support and locomotion without explicit spinal transmission of motor commands through the lesion. This is achieved with combinations of pharmacological and physical therapies that maximize cortical reorganization, inducing an expansion of trunk motor cortex and forepaw sensory cortex into the deafferented hindlimb cortex, associated with sprouting of corticospinal axons. Lesioning the reorganized cortex reverses the recovery. Adult rats can thus develop a novel cortical sensorimotor circuit that bypasses the lesion, probably through biomechanical coupling, to partly recover unassisted hindlimb locomotion after complete spinal cord injury. DOI:http://dx.doi.org/10.7554/eLife.23532.001
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Affiliation(s)
- Anitha Manohar
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, United States
| | - Guglielmo Foffani
- CINAC, Hospital Universitario HM Puerta del Sur, Universidad CEU-San Pablo, Madrid, Spain.,Hospital Nacional de Parapléjicos, Servicio de Salud de Castilla-La Mancha, Toledo, Spain
| | - Patrick D Ganzer
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, United States
| | - John R Bethea
- Department of Biology, Drexel University, Philadelphia, United States
| | - Karen A Moxon
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, United States.,Department of Biomedical Engineering, University of California, Davis, United States
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62
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Affiliation(s)
- Yue Li
- Burke Medical Research Institute, White Plains, New York, NY, USA
| | - Edmund R Hollis
- Burke Medical Research Institute, White Plains, New York, NY, USA.,Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY, USA
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63
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Hilton BJ, Moulson AJ, Tetzlaff W. Neuroprotection and secondary damage following spinal cord injury: concepts and methods. Neurosci Lett 2017; 652:3-10. [DOI: 10.1016/j.neulet.2016.12.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 11/28/2016] [Accepted: 12/02/2016] [Indexed: 01/29/2023]
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64
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Adler AF, Lee-Kubli C, Kumamaru H, Kadoya K, Tuszynski MH. Comprehensive Monosynaptic Rabies Virus Mapping of Host Connectivity with Neural Progenitor Grafts after Spinal Cord Injury. Stem Cell Reports 2017; 8:1525-1533. [PMID: 28479302 PMCID: PMC5469919 DOI: 10.1016/j.stemcr.2017.04.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 04/04/2017] [Accepted: 04/05/2017] [Indexed: 12/11/2022] Open
Abstract
Neural progenitor cells grafted to sites of spinal cord injury have supported electrophysiological and functional recovery in several studies. Mechanisms associated with graft-related improvements in outcome appear dependent on functional synaptic integration of graft and host systems, although the extent and diversity of synaptic integration of grafts with hosts are unknown. Using transgenic mouse spinal neural progenitor cell grafts expressing the TVA and G-protein components of the modified rabies virus system, we initiated monosynaptic tracing strictly from graft neurons placed in sites of cervical spinal cord injury. We find that graft neurons receive synaptic inputs from virtually every known host system that normally innervates the spinal cord, including numerous cortical, brainstem, spinal cord, and dorsal root ganglia inputs. Thus, implanted neural progenitor cells receive an extensive range of host neural inputs to the injury site, potentially enabling functional restoration across multiple systems.
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Affiliation(s)
- Andrew F Adler
- Department of Neurosciences, University of California - San Diego, La Jolla, CA 92093, USA
| | - Corinne Lee-Kubli
- Department of Neurosciences, University of California - San Diego, La Jolla, CA 92093, USA
| | - Hiromi Kumamaru
- Department of Neurosciences, University of California - San Diego, La Jolla, CA 92093, USA
| | - Ken Kadoya
- Department of Neurosciences, University of California - San Diego, La Jolla, CA 92093, USA
| | - Mark H Tuszynski
- Department of Neurosciences, University of California - San Diego, La Jolla, CA 92093, USA; Veterans Administration San Diego Healthcare System, San Diego, CA 92161, USA.
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65
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Tedeschi A, Bradke F. Spatial and temporal arrangement of neuronal intrinsic and extrinsic mechanisms controlling axon regeneration. Curr Opin Neurobiol 2016; 42:118-127. [PMID: 28039763 DOI: 10.1016/j.conb.2016.12.005] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 12/07/2016] [Accepted: 12/08/2016] [Indexed: 01/30/2023]
Abstract
Axon regeneration and neuronal tissue repair varies across animal lineages as well as in the mammalian central and peripheral nervous systems. While the peripheral nervous system retains the ability to self-repair, the majority of axons in the adult mammalian central nervous system (CNS) fail to reactivate intrinsic growth programs after injury. Recent findings, however, suggest that long-distance axon regeneration, neuronal circuit assembly and recovery of functions in the adult mammalian CNS are possible. Here, we discuss our current knowledge of the cell signaling pathways and networks controlling axon regeneration. In addition, we outline a number of combinatorial strategies that include among others microtubule-based treatments to foster regeneration and functional connectivity after CNS trauma.
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Affiliation(s)
- Andrea Tedeschi
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
| | - Frank Bradke
- German Center for Neurodegenerative Diseases (DZNE), Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.
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66
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Serradj N, Agger SF, Hollis ER. Corticospinal circuit plasticity in motor rehabilitation from spinal cord injury. Neurosci Lett 2016; 652:94-104. [PMID: 27939980 DOI: 10.1016/j.neulet.2016.12.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 11/29/2016] [Accepted: 12/02/2016] [Indexed: 11/18/2022]
Abstract
Restoring corticospinal function after spinal cord injury is a significant challenge as the corticospinal tract elicits no substantive, spontaneous regeneration, and its interruption leaves a permanent deficit. The corticospinal circuit serves multiple motor and sensory functions within the mammalian nervous system as the direct link between isocortex and spinal cord. Maturation of the corticospinal circuit involves the refinement of projections within the spinal cord and a subsequent refinement of motor maps within the cortex. The plasticity of these cortical motor maps mirrors the acquisition of skilled motor learning, and both the maps and motor skills are disrupted following injury to the corticospinal tract. The motor cortex exhibits the capacity to incorporate changes in corticospinal projections induced by both spontaneous and therapeutic-mediated plasticity of corticospinal axons through appropriate rehabilitation. An understanding of the mechanisms of corticospinal plasticity in motor learning will undoubtedly help inform strategies to improve motor rehabilitation after spinal cord injury.
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Affiliation(s)
- Najet Serradj
- Burke Medical Research Institute, White Plains, New York, NY 10605, United States
| | - Sydney F Agger
- Burke Medical Research Institute, White Plains, New York, NY 10605, United States
| | - Edmund R Hollis
- Burke Medical Research Institute, White Plains, New York, NY 10605, United States; Brain and Mind Research Institute, Weill Cornell Medical College, New York, NY 10065, United States.
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67
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Morales D, Kania A. Cooperation and crosstalk in axon guidance cue integration: Additivity, synergy, and fine-tuning in combinatorial signaling. Dev Neurobiol 2016; 77:891-904. [PMID: 27739221 DOI: 10.1002/dneu.22463] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 08/17/2016] [Accepted: 10/10/2016] [Indexed: 12/31/2022]
Abstract
Neural circuit development involves the coordinated growth and guidance of axons to their targets. Following the identification of many guidance cue molecules, recent experiments have focused on the interactions of their signaling cascades, which can be generally classified as additive or non-additive depending on the signal convergence point. While additive (parallel) signaling suggests limited molecular interaction between the pathways, non-additive signaling involves crosstalk between pathways and includes more complex synergistic, hierarchical, and permissive guidance cue relationships. Here the authors have attempted to classify recent studies that describe axon guidance signal integration according to these divisions. They also discuss the mechanistic implications of such interactions, as well as general ideas relating signal integration to the generation of diversity of axon guidance responses. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 891-904, 2017.
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Affiliation(s)
- Daniel Morales
- Institut de recherches cliniques de Montréal (IRCM), Montréal, Quebec, H2W 1R7, Canada.,Integrated Program in Neuroscience, McGill University, Montréal, Quebec, H3A 2B4, Canada
| | - Artur Kania
- Institut de recherches cliniques de Montréal (IRCM), Montréal, Quebec, H2W 1R7, Canada.,Integrated Program in Neuroscience, McGill University, Montréal, Quebec, H3A 2B4, Canada.,Department of Anatomy and Cell Biology, Division of Experimental Medicine, McGill University, Montréal, Quebec, H3A 2B2, Canada.,Department of Biology, Division of Experimental Medicine, McGill University, Montréal, Quebec, H3A 2B2, Canada.,Faculté de Médecine, Université de Montréal, Montréal, Quebec, H3C 3J7, Canada
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68
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Steward O, Willenberg R. Rodent spinal cord injury models for studies of axon regeneration. Exp Neurol 2016; 287:374-383. [PMID: 27374113 DOI: 10.1016/j.expneurol.2016.06.029] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 06/28/2016] [Indexed: 11/29/2022]
Abstract
For over a century, axon regeneration has been considered the Holy Grail for spinal cord injury (SCI) repair. Although there are other factors that could contribute to improving function, restoring the long motor and sensory tracts that are interrupted by SCI has the greatest potential for actually reversing paralysis, restoring the brain's control of autonomic functions mediated by sympathetic and parasympathetic circuits of the spinal cord and restoring sensation. Accordingly and in keeping with the overall theme of this special issue, this review focuses narrowly on rodent SCI models for studies of axon regeneration.
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Affiliation(s)
- Oswald Steward
- Reeve-Irvine Research Center, University of California at Irvine, Irvine, CA 92697, United States; Department of Anatomy & Neurobiology, University of California at Irvine, Irvine, CA 92697, United States; Department of Neurobiology & Behavior, University of California at Irvine, Irvine, CA 92697, United States; Center for the Neurobiology of Learning and Memory, University of California at Irvine, Irvine, CA 92697, United States; Department of Neurosurgery, University of California at Irvine, Irvine, CA 92697, United States.
| | - Rafer Willenberg
- Reeve-Irvine Research Center, University of California at Irvine, Irvine, CA 92697, United States; Department of Anatomy & Neurobiology, University of California at Irvine, Irvine, CA 92697, United States; University of California at San Diego, School of Medicine, San Diego, CA 92093, United States
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